1. Field of the Invention
The present invention is generally concerned with torsional damper devices comprising at least two coaxial parts disposed to rotate relative to one another within defined limits of relative angular movement against elastic means, commonly called circumferentially acting elastic means, operative circumferentially between them for at least part of such relative angular movement.
2. Description of the Prior Art
As is known, this type of torsional damper device is normally incorporated in the design of a clutch disk, particularly for automobile vehicles, in which case one of the rotary parts carries a friction disk designed to be constrained to rotate with a first shaft, in practice a driving shaft and the motor output shaft in the case of an automobile vehicle, whereas another of said rotary parts is carried on a hub designed to be constrained to rotate with a second shaft, in practice a driven shaft and the gearbox input shaft in the case of an automobile vehicle.
This type of device is used to permit regulated transmission of rotational torque applied to one of its rotary parts where the other is itself subject to a rotational torque, in other words to filter vibrations which may arise at any point in the kinematic system in which it is incorporated, extending from the motor to the driven road wheels in the case of an automobile vehicle.
The present invention is more particularly directed to the case where at least three coaxial parts are employed in a torsional damper device of this kind, said coaxial parts being as previously disposed to rotate relative to one another in pairs within defined limits of relative angular movement against circumferentially acting elastic means operative between them for at least part of such relative angular movement.
These are, in practice, a hub, at least one flange, commonly called the hub flange, constituting a transverse annular member around the hub with, between it and said hub, meshing means implemented with clearance, and at least one ring, commonly called the guide ring, parallel to said hub flange and like the latter forming a transverse annular member around the hub, but independent of the latter.
Between the hub and the hub flange there is formed a first damper stage, a second damper stage being formed between the hub flange and the guide ring or rings.
In the case of a clutch disk, it is the guide ring or rings which more often than not carry the friction disk.
As is known, it is advantageous in certain applications at least, and particularly in those relating to clutch disks for automobile vehicles, for the circumferentially acting elastic means employed between the hub flange and the hub to be low stiffness elastic means.
As is known per se, at low values of torque this arrangement as applied to clutch disks for automobile vehicles advantageously enables gearbox neutral setting noise to be eliminated when the vehicle is stopped, especially when warmed up.
Usually, however, this arrangement has an unfortunate side effect in that it is itself the cause of another type of noise, commonly referred to as a "clunk", when, as applied to an automobile vehicle clutch disk, the driver of the vehicle releases, more or less suddenly, the pressure previously exerted on the accelerator of the vehicle, the operation of the assembly then changing from the so-called "upshift" mode, in which the motor torque predominates over the resisting torque, to the so-called "downshift" mode, in which conditions are the reverse of those applying previously.
The circumferentially acting elastic means disposed between the hub flange and the hub are very rapidly saturated, being of low stiffness. Because of this, there is each time a virtually instantaneous and therefore noisy rocking movement of the hub flange relative to the hub, corresponding to a change in the bearing engagement, from one circumferential direction to the other, between the meshing means with clearance operative between said hub flange and said hub, due to expansion of said circumferentially acting elastic means, previously saturated in a first circumferential direction, followed by renewed saturation of the latter in the opposite circumferential direction.
This "clunk" noise, which also occurs when the accelerator is pressed again, is particularly bothersome when the vehicle is being driven "in traffic", that is to say in the way which may occur in town driving, for example, where the speed of the vehicle is low, possibly near the normal idling speed of the motor, for example, and the torque required from the motor is also low, the motors currently fitted to certain vehicles actually being designed to be able to function under such operating conditions in order to minimize fuel consumption.
Furthermore, it may be accompanied by a rocking movement which, transmitted to the motor and through this to the body of the vehicle concerned, may cause oscillatory movement of the body, especially when the motor is disposed transversely relative to the body, this movement due to the change of direction of the torque being likely to cause discomfort to the driver of the vehicle.
Various solutions intended to alleviate these disadvantages have been proposed, in particular in French patent application No 79 04719 filed 23 Feb. 1979 and published under the number 2 449 828.
According to certain of these proposals, in the general case of a torsional damper device comprising at least two coaxial parts disposed to rotate relative to one another, there is employed a locking member which is responsive to centrifugal force and which, beyond a defined or critical speed of rotation, systematically takes out of service the low stiffness portion of the circumferentially acting elastic means disposed between said rotary parts.
However, as the locking action obtained by means of a locking member of this kind is a positive one, said locking member carries at least temporarily the full torque to be transmitted between the rotary parts concerned.
The value of this torque is not necessarily known, especially when operating under "downshift" conditions, and may be very high.
It is not rare, given these conditions, for sudden breakage of a locking member of this kind to occur.
According to other arrangements described in the aforementioned French patent application No 79 04719, there is employed instead of a locking member an intermediary member also responsive to centrifugal force disposed to move between a standby position in which it is inoperative and, beyond a defined or critical speed of rotation, an operative position in which, being operative between the two rotary parts concerned, for at least one direction of relative rotation between them, it urges in said rotation direction for low values of torque circumferentially acting elastic means other than those normally operative between these rotary parts at the low values of torque concerned, in cooperation with return means continuously urging it towards its standby position.
In other words, by virtue of this intermediary member, the low stiffness circumferentially acting elastic means normally operative between the two rotary parts at low values of torque are prevented from acting alone when said intermediary member is in its operative position and the torque to which this intermediary member is then subjected is moderate and its value well-defined, since it corresponds to part only of the high stiffness circumferentially acting elastic means also disposed between said rotary parts.
In practice, however, the arrangements described in this connection in the aforementioned French patent application No 79 04719 relate to torsional damper devices comprising only two rotary parts.
They can only with difficulty be applied to torsional damper devices comprising at least three such rotary parts.
A general object of the present invention in an arrangement specifically intended for torsional damper devices of this kind.